About 20,000 people are feared dead after a volcanic eruption in northern Colombia.

Four towns in the Andes region are reported to have been buried when ash spewed out of the volcano, Nevado del Ruiz, causing a mudslide.

The worst-affected was Armero, the province of Tolima's second largest city, about 50 miles from the Colombian capital, Bogota.

Armero, which lay in a valley below the 16,200-foot high (4,937m) volcano, was virtually destroyed - buried by mud and rubble swept down on to it.

The fatal eruption happened during the night when most of the town's 27,000 residents were in bed.

Nevado del Ruiz, known locally as "the Sleeping Lion", had not erupted for nearly 150 years.

Increased activity

Even though it is located only 310 miles (500 km) from the equator, the volcano's summit is covered with snow.

It had given some warning of increased activity - in recent months there had been some rumblings from the crater - but the authorities had told Armero residents it was safe to remain in the city.

The initial blast began on Wednesday afternoon when ash came showering down.

An evacuation was ordered but abandoned when the volcano went quiet at about 1900 local time.

However, just after 2100 a more serious eruption began causing the summit's icecap to melt and carry mud and debris down the mountain at speeds of up to 30 miles (50 km) per hour.

The town of Armero lay in the so-called "Ring of Fire", an unstable area of the earth's crust encircling the Pacific Ocean which includes most of the world's active volcanoes.

The Colombian government has appealed to the United Nations for help.

However, rescue efforts are being hampered by fallen bridges and impassable roads.

In Context
The final death toll was estimated at 23,000.

It was the second most deadly eruption in the 20th century after the 1902 eruption of Mont Pelee on the Caribbean island of Martinique which killed 29,000 people.

Following the 1985 eruption, Nevado del Ruiz remained active for several more years, culminating in eruptions in 1991 and 1992.

It was not the first time the volcano had caused deaths.

In 1595, 636 people were killed after a mudflow swept down the mountainside. Another eruption in 1845 led to 1,000 deaths.

Around 50 years later settlers began to build the city of Armero directly on top of the hardened mudflow deposits.
After the 1985 disaster the government declared the site of the buried city to be "holy ground".